Hopefully 15% is no longer the max allowed by the plan - larger company could mean better 401K. Could also mean worse or the same.
There are many factors, but contributing at least enough to get the match is almost never a bad choice. After that point, you've got to look at the options in the plan, your tax rates, the total amount you want invest each year, and decide. Then the usual assess your risk tolerance and pick an asset allocation accordingly always applies.