Here’s the explanation from Jeff at Navionics. I know this is not going to make x15 owners happy but at least it’s an honest explanation and it does make sense. Thanks for the info Jeff.
Here it is:
Hi Wade,
FYI regarding the LCX-15 and Premium compatibility. The LCX-15 uses an older (but still good) processor than the
new units. I think the 15 has been on the market for about 5 years now (thats like 150 in dog years with electronics)! The problem is that Premium requires a MASSIVE ammount of memory and processing speed. The X-15 would simply choke on Premium because it supports neither. HotMaps ran on a 16MB cartridge (which you can barely buy anymore)-Premium needs at least a 64. – Jeff