Is 2 ml of Profhilo enough for a good result?

Standard use of Profhilo calls for injecting 0.2ml in each of the 10 points (5 on each side) each session. This totals to 4ml of Profhilo used over 2 sessions. 
I don't see the benefit of injecting less than the standard amount as you risk losing some of the results of the treatment with no potential gain, other than a slightly cheaper bill. It is never worth sacrificing quality of treatment for a lower price.
It may be in your best interests to get a secondary opinion in a consultation with another trained professional if you are not feeling 100% comfortable.

Profhilo is uncrosslinked hyaluronic acid intended to stimulate the skin to create new collagen. The fact that it is uncrosslinked means that the body will absorb it quickly. If you are going to use it, you need to do something else to stimulate the body to make collagen. I use a crosslinked filler like Juvederm Volbella just under the skin to do this in people with significant wrinkles. However, I also stimulate the skin, especially in anyone over 25-30 where the skin stops making collagen on its own, to make new collagen using tretinoin (Retin-A) or retinol. Use of minroneedling or a fraxel laser also works. At 30, your best bet is to add Retin-A or retinol to your basic skin care which should be a cleanser, a pH balancer, an exfoliant and a zinc oxide sunblock of 8% or more. Adding Obagi's ELASTIderm to convert some new collagen to elastic tissue also helps.