You could follow the instructions on this page: Converting older FileMaker Pro files to the .fmp12 file format | FileMaker
It has links to download trial versions of FileMaker Pro 6 and FileMaker Pro 11 which you will need to do the conversions to bring it up to .fp7 format. You can then use FileMaker Pro 12 or newer to convert it up to the current .fmp12 format which v13 uses....
I'm happy to do it for you if you would like to PM me with the file...
Given the extreme number of revisions between then and now, it may be simpler and more effective to simply export your data to a tab, csv or merge file (not sure which would be supported back then) and then you import this data with the new table option to create new tables in FileMaker 15.
This only imports your data, no calculation definitions or layouts, but much of this is likely to need reworking and review anyway after conversion so it may prove more effective in the long run.
True, though doing this assumes you have an old copy of FileMaker 1 - 2 (these files really were that old!) running on an old machine or emulator or something so that you can do the exports, which in this case I didn't have to hand, so it was easier to just get the trial of FileMaker Pro 6 running in Windows to convert to .fp5 - getting FMP 6 running on Mac more tricky as I think it is PowerPC only, so would need a Mac running Mac OS 10.5 or earlier. From getting it up to .fp5, for me on macOS Sierra 10.12, then using FMP11 to convert it to .fp7 and FMP15 to convert that to .fmp12 was easily done.
As these files really were very simple ones with just 3-4 layouts, no scripts, and very basic field definitions (no calculation fields), they survived the conversions up to .fmp12 without any problems, though yes, I agree that rebuilding the files from fresh using current version FileMaker would be best for a more mission critical system.