1. it depends on what programs you want to save. If the 15gb has almost the same, that's one issue. If you have the installation files saved or availible, that's easier.
2. slave the 8gb to the 15gb as the master on the new machine. When asked for drivers for the different harware, explore to the 8gb Windows\INF and sometimes INF\other. If a file isn't found, use "find" and search the 8gb only. Some hardware, regardless, asks for original install files. You may have to hunt and load Mobo Chipset drivers, as W98SE puts in generic ones that will work but may not be all of them, and I haven't had great success at finding Southbridge drivers in the old folder. They often are needed for the onboard video or audio.
3. The other thing I do is start the new PC with different Hdd in Safe Mode, to look at all device "aliases" that came over with old 15gb load, and remove the devices, if they are not of the new PC. Since I test and slave many Hdd's and CDrom drives, I may have 30 ro more unnecessary listings. Generally, they don't bother 98 as it will look at and load only what is detected, and why you don't see aliases in normal boot.
That's why you don't have to delete the registry entry stated.
4. The best and easiest thing to do with the 8gb on newer PC is to get a cheap 8gb or more used drive and slave it to the current 8gb. Then transfer all data type files, such as MP3 or such. I can't imagine loading a W98SE 8gb Hdd with that many Program type files that can't really be easily transferred to the new (used) 8gb added on as storage. It usually means you have a lot in the old 8gb that could be cleaned.
5. if this is confusing, ask more, and indicate what is taking up so much space on the 8gb.