How easily does it start? If it's starting all right then I can't see either ether content or compression being the problem. The figures quoted seem way low, even for a worn-out engine.

If it can do 15500 in standard glow form, I can't see that Fox would be particularly sympathetic.

Out of interest, have you tried something like an 8x4, 8x6 or 9x4 with it running as a diesel? 9x6 and 10x6 are both more than I would normally use for a .15 (I fly CL), so I'm wondering how it would go on a smaller prop.