Well, in that case you aren't gaining a huge amount by leaving it in your 401(k). In fact, you will be paying a (negligibly) higher amount in fees. You get some added protection from lawsuits by keeping that money in your 401(k) vs in your tIRA. It's also a tiny bit easier to access that money if you are laid off and/or retire at age 55 than it is for your tIRA.
But you'll have no say if your former company decides to change retirement plans, and it's just another account to keep track of.
Ultimately: your call. I'd favor rolling it over today just to keep it simple, but I value simplicity over +0.005% in annual fees.