True, empowered it's (1d6+4)x1.5, max of 15 damage.
However, you're getting between 32 and 36 tentacles. That's a lot of tentacles. Assuming you've got 4 party members, that's still a potential of 135 damage to each party member every round that they are within the tentacles. For a level "6" spell, not too shabby. This is also assuming the wizard was stupid and didn't open with a mord or greater dispell, sure, the bard/other wizard may live. Assuming the entire party has a brawler's belt or item to that effect(because they are so common post-grandfathered Ravenloft), that brings it down to the normal 5 damage. A stoneskin will also help, but will break very quickly, since it's just HP.
This spell is ridiculously deadly when used by the right hands, because it lasts so long, and is a fairly low level spell, so it is spammable even when empowered. In a high-magic setting, the spell is fairly underwhelming because everyone can get 15 DR that isn't breakable, but in a low magic setting like Ravenloft, prepare for tentacle rape. That, and the majority of people are below level 15... even in the hands of a relatively low level wizard, the spell is still really scary. A level 11 wizard, capable of casting Evard's empowered - he still can get 22 tentacles, as if he was casting the spell at level 20 regularly. Not bad at all.
But hey, if you don't believe me...