I do normally use starter but have mistakenly developed without starter several times. No problem.

I don't use the Digibase chems but the C41 process is fairly standard so I'd guess you're ok.

My understanding of starters in general is that they are designed to make newly mixed chems act like chems that have been replenished awhile. It is for consistency.

Without the starter the developer may work a bit quicker. Even if that is true I'd still stick with 3:15.