API 15S was a JIP output. However it is not a spec, just recommended practice. With recent development in composite pipe, RTP is not just kevlar reinforced thermoplastic, but also glas fibre, combined glas - kevlar reinforcement, bonded and unbonded structure. They are trying hard to fit in API 17B, 17J & K. I know the limitation to temperature, long term strength, non plastis burst, permeation issue, etc. But still cannot understand why onshore application is allowed, but offshore is explicitly prohibited.
Agree with SJones, for offshore use, additional requirement may apply. In my thought are collapse and buckle, tension, torsion, on bottom stability, installation, external impact, etc, similar to steel pipe.
However, the main code, B31.4&8 is explicitly prohibit it for use in offshore.