You also may want to think about what your final format will be. If you’re going out to DVD you might want to go ahead and convert them to DV and edit them that way. There should be no trouble since you’re going from 15 to 30 so each frame will be doubled.
I usually work in DV and last week a guy brought me some image sequences of an architectural 3D fly-through that he needed pieced together. They were 24fps, which I thought would be no big deal since I could combine each of the image sequences into a movie then edit in 24fps in FCP. They were also 1024×768, also no big deal since they were the right aspect ratio.
I had no problem combining the image sequences into movies with QT. I had no problem editing in FCP in 24fps 1024×768. I ran into problems when I exported the movie for DVD. I got a glitch every place I had an edit. I never could figure out why. Under a hard deadline, I decided to convert all the 24fps movie pieces to DV so I could re-edit in that format. It worked but the results were less than stellar. I converted them using the open source VisualHub because it does it so quickly. (good, fast, cheap, pick two) That was my mistake, the client was not pleased with the slight stuttering effect that the conversion from 24 to 29.97 produced. So after further research I happened upon an old ally Ken Stone and he pointed me in the right direction on doing a proper conversion. Hope this ramble helps.
https://www.kenstone.net/fcp_homepage/converting_frame_rates_compressor.html
DT Motion Pictures
https://www.davetaylormp.com