Not Brightest Blip On Radar Screen

Scenario:- VFR flight from Antigua TAPA to Martinique TFFF using gps and autopilot for altitude and nav.
Navigation log flight level 15.
Believing this to represent 1500 feet as 150 = 15000 feet and ac i'm flying has a max level of 14500 i happily proceed on my way.
While leaving the ac on auto pilot to get a coffee i slam into a hilltop in Dominica. So much for 15 or 1500 feet on nav log.
Can not find a decent explanation of altitudes in help areas.
Would someone help me out here as to flight levels.
Thanks

Navigation log flight level 15.
Believing this to represent 1500 feet as 150 = 15000 feet and ac i'm flying has a max level of 14500 i happily proceed on my way.
While leaving the ac on auto pilot to get a coffee i slam into a hilltop in Dominica. So much for 15 or 1500 feet on nav log.
Can not find a decent explanation of altitudes in help areas.
Would someone help me out here as to flight levels.
Thanks
