Like everyone else has said, the promoters might be telling you "15 minutes max" for changeovers and really scheduling the event so there's a cushion of time if things get behind…but count on it being a nightmare anyway (and be pleasantly surprised if it works out).
This right here is a great way to help minimize your share of chaos in a fast changeover, but I would add two important caveats: if you're providing the backline bass rig then make sure everyone is in agreement in how you want your gear treated, and you reserve the right to make changes to the amp (even mid-song) if you feel your gear is being damaged in any way.
I've routinely offered and let my gear be used as a backline at shows with more than three bands if we're headlining or direct support, as I've taken it upon myself to be a non-official Bergantino ambassador to my circles in Texas. Most of the time other musicians are cool and respectful, but in one instance a bassist decided to send as loud a signal from his 18v active bass and pedalboard into my amp as he could. I was a block away picking up some pizza and when I walked back into the venue I could hear a gnarly distortion that was definitely my amp's preamp clipping and speakers being pushed too hard. Miraculously nothing was permanently damaged but I have no idea how long he'd been pushing my rig that way and that guy is on my list of "never again, go get your amp out of the trailer".
It is doable and all the previous suggestions will help. I will also add if you can talk to the other bands bass players and/or the engineer prior it may help?
I did a charity gig in a "throw" together band a few years back that had 6 bands. We were 4th on the bill (great cause and raised a lot of money as it was an expensive ticket.) Before the show date I was told who had volunteered to be the engineer and knew him (not well, but had worked with him before years ago) and let him know I was able to provide a bass amp to everyone to use as the back line all evening. He agreed knowing what it was and the decision was made and all the bass players were advised. Every bass player was very happy not having the bring and move theirs. If you can get any of the bands to agree to share gear, it will help on change over and as others said, be ready and be prepared that it may go overtime.
This right here is a great way to help minimize your share of chaos in a fast changeover, but I would add two important caveats: if you're providing the backline bass rig then make sure everyone is in agreement in how you want your gear treated, and you reserve the right to make changes to the amp (even mid-song) if you feel your gear is being damaged in any way.
I've routinely offered and let my gear be used as a backline at shows with more than three bands if we're headlining or direct support, as I've taken it upon myself to be a non-official Bergantino ambassador to my circles in Texas. Most of the time other musicians are cool and respectful, but in one instance a bassist decided to send as loud a signal from his 18v active bass and pedalboard into my amp as he could. I was a block away picking up some pizza and when I walked back into the venue I could hear a gnarly distortion that was definitely my amp's preamp clipping and speakers being pushed too hard. Miraculously nothing was permanently damaged but I have no idea how long he'd been pushing my rig that way and that guy is on my list of "never again, go get your amp out of the trailer".