Wirelessly posted (Opera/9.80 (BREW; Opera Mini/6.0.3/27.2338; U; en) Presto/2.8.119 320X240 LG VN530)
On channels 1-7, the radio you are using will determine what rules you must follow. IIRC, some of the hybrid radios were capable of more than 0.5 watts (500 milliwatts) on those seven channels. If so, then you must follow the GMRS rules, even if you use the low power option, as an FRS radio cannot be capable of greater than 500 milliwatts ERP. (Also, although I'm unaware of any bubblepack radios with a detachable antenna, if the antenna is capable of detaching from the radio, you must follow the GMRS rules, as FRS radios are prohibited from having a detachable antenna.)
And I'd like to know where people keep getting this 15 watt ERP limit from? FRS radios have a 0.5 watt (500 milliwatt) ERP limit on all 14 FRS channels. GMRS radios have a 5 watt ERP limit when using channels 1-7, regardless if it's a handheld, mobile, or small base station. On channels 15-22 (462.550, .575, .600, etc) you can use up to 50 watts transmitted power output, whatever your radio make & model is capable of, with no ERP limit.
Edit: Are you referring to the archaic Fixed Stations? They had some severe restrictions imposed upon them. They were prohibited from being located within any large urban area; they were restricted to using a directional antenna with a minimum 15 decibel front-to-back ratio; were limited to 15 watts TPO; and lastly, were only allowed to communicate with another fixed station.
What were fixed stations used for? Base stations were not allowed to talk to each other. If you had a need to talk house-to-house across town, (assuming your town wasn't a part of a large urban area as defined by the FCC in Appendix B) you had to license them as fixed stations. (If you go back about 15 years, you'll see them referred to at 95.21(b), 95.29(g), 95.47, 95.49 and 95.61.)
Bottom line, don't worry about fixed stations, or the 15 watt ERP limit. It will not affect you.