Hi pandaos, welcome to CDFreaks!
It’s difficult to answer your question exactly without knowing if HJ-Split uses decimal or binary prefixes, i.o.w. whether it thinks 1 kB = 1000 B (decimal prefix) or 1 kB = 1024 (binary prefix), and whether your 19 “GB” file uses the binary or decimal definition of G (Giga).
Let’s use this definition:
MiB = 1024 KiB = 1024x1024 B
A DVD will hold at least 4.700.000.000 bytes, and the most usual sizes are 4482 MiB for DVD+R and 4489 MiB for DVD-R
Assuming worst case scenario, 3 times 19x1024^3 bytes file and HJ-Split using binary prefix, you have 58368 MB to split into parts fitting on 4482 MB DVD+R discs or 4489 DVD-R discs (using binary definition of MB), which will take 14 discs (perhaps 13 if you’re lucky).
It’s hardly worth the calculation to try and find the right split sizes to achieve the optimal split onto 13-14 discs, so instead I would split each file into 10 parts using 2000 MB as a split size and burn two on each DVD on 15 discs.
It’s possible to get a better fit but I’m not doing that calculation for you.
EDIT: Great - the original poster changed his mind while I was typing my reply.