No, it is overpowered
As you've stated in your question, you have modeled this homebrew after the Orc and half-orc races.
Half-Orc Race Comparison
Ability Scores - Homebrew race provides a negative modifier to Intelligence. These are normally reserved for monstrous races, but that's okay. Intelligence isn't used that often, so it's a hindrance, but not an enormous one.
Size - equivalent
Speed - equivalent and skill proficiency is similar to menacing trait
Darkvision - equivalent
Undying - this is a pretty big deal that refreshes on short rest. The Half-Orc's Relentless Endurance is your comparison trait, but that only references on a long rest. Being able to do that after a short rest is a big boost.
Immunities/resistance - Half-Orc has none, this is another feature granting significantly more power.
The Half-Orc does have their Savage Attack additional crit damage die, but that only happens on a crit and only adds a single die. It is not equivalent to resistances or short rest Undying.
Orc Race Comparison
Before we get into this specific comparison, there is a caveat that WoTC included in Volo's regarding monstrous races:
Some of these races are unusual in that they have a reduction to an ability score, and some are more or less powerful than the typical D&D races.
Utilizing these as a basis for creating homebrew may not be the best methodology. The comparison above against the Half-Orc may be better or see my note on reskinning of the Warforged Race at the end.
Ability Scores - equivalent
Size - equivalent
Speed - equivalent and skill proficiency is similar to Orc's menacing trait
Darkvision - equivalent
Undying - this is a pretty big deal that refreshes on short rest. It's similar to the Barbarian's 11th level class feature, but without even needing a save. This is likely overpowered.
Immunities/resistance - Orc has none, this is another feature granting significantly more power.
The Orc does have their Aggressive Bonus action trait, but that's granting more movement to move towards an enemy and is much less powerful than either Undying or immunities.
Overall Assessment
The Undying and Immunities traits make this race much more powerful than the comparable races you've modeled your homebrew after and they are not balanced by the minimal impact negative INT score.
If you really want to add the Undying trait, then modelling your design after the Half-Orc will likely give you a better starting point since they have that trait (including the Long Rest refresh only). This would also allow you to remove the negative INT modifier (which isn't really that big of a deal given the small number of INT saves.)
In which case, the equivalent mechanic you're trying to find/create is that of the Savage Attack. However, Resistance to damage is definitely not that and is generally more powerful than an additional damage die you get approximately 1 in 20 attack rolls.
Take a look at the Warforged
As a sidenote, you may want to also look at the Warforged race for inspiration (or reskinning) as these are very similar to what you're describing.
Warforged are formed from a blend of organic and inorganic materials...While they’re formed from stone and steel, warforged are living humanoids.
This very much has a 'created human' feel to it. You'd just be reskinning the stone/steel with some other background fluff.
Some of your verbiage is a little odd, and I have a couple changes, but it should be
Balanced for general play
This feels like you went off of the Lizardfolk as a template (not a criticism, it's where I would have started). I think this is pretty well done and I wouldn't have an issue playing alongside it at my table.
ASI, Speed, Vision, Languages, and Size are all standard - so I'm not going to talk further on it.
- Bite is fine. It's really not going to get that much use.
- Rampage I think that rampage being limited to your bite attack is important here.
- Heart of the Hunt is clunky and I'd recommend it being proficiency instead. Not many traits give expertise (it's usually advantage) and also it's a niche application. Maybe Proficiency in Wisdom (Survival).
- Keen Senses is also clunky. I know the Loxodon has this, but that's an entire extra appendage and the schtick of the race; the standard way to do for player races it is to give a proficiency in Wisdom (Perception). Advantage on scent checks and the like is more for monsters - and even then it's just "Wisdom (Perception) related to Smell/Hearing".
To reiterate: I don't think that Heart of the Hunt is terribly strong, but it's just not going to get much use as you have it. I have never ever had to roll Strength (Athletics) to run or chase and I haven't seen anyone do it either. Keen Senses is a little stronger than I'd like and I do recommend toning it down, but my issue is that it feels out of place. That's not to say that you can break the mold a little bit when making new things, but there should be some consistency in feeling across abilities across races.
Best Answer
Thumbs up
This seems pretty balanced and cleanly written. Using Detect Balance, a tool that has pooled a lot of community input to grade the power of various racial abilities on a point scale, this scores as:
Total: 25-26 points, the recommended range is 24-27, the average of the PHB races is 25.
Certainly not over the top.
If I would have one minor qualm, then it is the framing as “younger” Oni. Oni is a type of giant, and younger ones that do not yet have grown into their full powers are still just Oni.
You also might consider changing Silent Image for Disguise Self, because a full blown Oni has a strong ability to alter their own form, but cannot cast Silent Image.
1 It could be stronger on a build that tries to hit for nova damage. Detect Balance assigns 8 points to unlimited advantage on a very common roll, and it this limited variant must be worth a good bit less.