I haven't spent any money on Boom Beach either, but it can take over 2 hours to train troops if you're at max level using all tanks (4 per boat at 36 minutes each = 144 minutes).
You can only get 3 per boat at max size. Level 20 landing craft have 24 seats, tanks take 8 slots.
3 tanks does take a long time but every other unit trains in a fraction of the time tanks do. Tanks take longer because you will often take no casualties with them.
3 tanks does take a long time but every other unit trains in a fraction of the time tanks do. Tanks take longer because you will often take no casualties with them.