Yes - massively so! You'll get horrendous diffraction limiting the resolution of the print. The odd stop or two will probably be okay (especially for smaller enlargements), but going all the way to minimum aperture will be dreadful. Try ND filtration to reduce the effective output of the enlarger if you really need to lengthen exposure times. If you've got a colour head you might be able to achieve what you want by dialing in equal amounts of cyan, yellow, and magenta filters. However if you're printing on multigrade papers either of these methods might result in unintended slight shifts in grade - just have to suck it and see.