Electrical wiring question - How can I get 1300 watts x2 from a 15 ampere breaker by splitting amp
Hire an electrician before you burn your shop down with all those computers in it.

While I can try to educate you, the fact that there's PLENTY of information already available and yet you clearly have done no research or just don't understand your power system makes the above my succinct advice.

In short, neutral has nothing to do with a 240V (only) circuit in the USA/Canada system.

You replace two 15A one-space breakers with one 15 amp two-space breaker, and both legs are hot. You need to replace the receptacles on the circuits as well.

Alternatively just add 4 more single-pole 15A breakers and wire new 120VAC circuits to them.

Please hire an electrician rather than forge ahead half-understanding; or take a good long time to actually understand before you touch a wire.