You'll be fine as long as you don't overpower your speaker AND don't clip your amp.
If you send too much power to the speakers, you can cause thermal damage.
If your amp is underpowered (and I wouldn't think 150 WPC is generally underpowered, unless it's some type of cheapo receiver), then you run the risk of trying to get too much out if, which leads to clipping, which leads to a skewed frequency spectrum, which will most likely damage your tweeters. The clipping will cause high frequency components to be artificially generated, with the potential of much more energy going to the tweeters than should. Of course, you can also kill components other than tweeters with this method.
In general, if you find yourself thinking "this sounds like crap" because it's distorting, raggedy, or otherwise unclear, you should probably turn it down. When those things happen, it's either the speaker or the amp that's under stress, and that's when damage is going to occur.
If you're never listening at high volumes, none of this should be a problem at all.
Good luck!
