The 2.5D will handle 5s fine, but may be a little much for the track. Neu 15xx motors are rated for up to 60,000 rpm although they run best in the 30-50k range. For 5s I would recommend getting the 1.5y which is 1850 kv. Some people also run the 3D (1700kv) on 5s, but Y winds theoretically are a little bit more efficient. But either of the motors you choose will run cool on 5s so overheating shouldn't be an issue.
My vehicles (that work):
Custom experimental Losi 810/TEN SCTE - The fastest 1/8 scale buggy on the track - 5.2lb rtr - readily convertable to a ROAR legal 1/10 scale 4x4 SCT.
Custom Losi 8ight - lowest CG of any 1/8 buggy
Losi 22 Mid Motor