Swap in a conventional switch to replace the dimmer. That is a sure cure.
Personally, the bath is the place where I do not want a dimmer.
If you really want this setup, try a different dimmer or experiment with different lamps.

You could try leaving the lamps on for about 100 hours and then see if they will dim down to a lower level without flickering.

If that doesn't work, try another brand of lamps. I only buy FEITs when I'm more concerned about price than quality.

CFLs are not going to dim like incandescent light, even if you have a 'dimmable' CFL or dimming ballast.

The difference in operation (discharge light vs. thermal heating) prevents any fluorescent from dimming as far.

since all the lamps in the store are inexpensive, do you think going online and buying a more expensive brand might solve the problem

A quick search for Feit 15 watt CFLs at HD brings up a product with a package that states "works on most dimmers."

Well, I guess there's their out - "most dimmers." You can try a dimmer that also indicates it's for dimmable CFLs or a different brand CFL.

Most OEM manufacturers now have just moved on to LED bulbs and really have no interest in improving their CFL designs.