What do you want? Heal yourself + 150HP every 15 secs? 
I dont know why im trying to answer your question, but anyhow here it goes
No, im thinking about a "mana" like system, so one can continuesly heal while he has supplies left BUT limit the amount healed per use of the skill. FA in the original fallouts werent as OPas they are here, i can easily recover from 2 minigun bursts with full hp..(107 max hp atm)
I was thinking about less cd, less gained hp...
Like a CD system if the devs love CDs that much:
A new kind of FA "CD" that counts as maximum "mana", would be calculated from INT and FA+doctor skill of a character. Multiply int by 10, add doc/2, add FA/2, or whatever, needs testing to be balanced ofc. If a player uses the skill, the amount healed would be substracted directly from the manapool. One use of FA would only heal a lesser amount, 200 skill would only heal for a mere max of 100 hp. Or whatever, numbers can be tweaked easily, its the underlying mechanics thats important.. When the manapool isnt full, i++ every sec. If the player has his FA CD on 30, with a skill of 300, he can only heal for 30. But 5 seconds later when his AP is regenerated, he can heal again, for 5 hp, etc... Optionally increase the AP requirements of FA, and there you have it, its balanced because the doc needs to continually heal himself or others just to stay alive, and cant do anything other himself. Also, lower the XP gained from FA and doc, or add diminishing to it because its too easy to level.
Example battle situation with current mechanics: 8 int, 114% FA. Thats actually my character atm. Im battling a minigunner. I have 107 hp. After the first burst i lost 60+ hp. Seeing as the next burst would ultimately result in my death i quickly FA myself to full hp, but only healed 60... Almost half of the amount i am capable of healing was wasted. After that i go full auto and manage to inflict 60 dmg. And then i die. And i only have 114 FA how about dedicated docs with 200-300 skill? Everybody is killed in 1-20 seconds -realtime- in this game, so lowering CDs just wont make the doc any more usefull..
But lets review the situation with the new system in place: 8 int means 240 CD. Incoming enemy burst, ~60 dmg, i heal ~60. CD at 180. Because i dont have enough AP(FA now costing 5 AP), i cant attack, i am forced to wait. Second burst is a crit, im hit for 100. I quickly heal for ~60 so im at 70 hp, CD at 120. The next 2 bursts were lucky ones again(60-60), and managed to heal myself for 50-50 each. CD at 20. Last burst, 60 again, 1-2 hp, but managed to attack once because bursting costs more AP for my opponent, so i managed to squeze in an attack. What luck! Hes out of ammo and needs to reload! Managed to attack again! In total i made a whopping 20 dmg, and my opponent suffered greatly. And then i got sawed in half. Yes i healed "150 hp every 15 seconds", and still died. In a big battle like NCR defense i would have managed to save 5 people, but is it overpowered? I dont think so. If it is, just play with the numbers a bit(starting CD-manapool calculation buff/nerf, max amount of heal per FA buff/nerf, AP needed to use FA buff/nerf, etc.)
But this is getting very offtopick... I beg for mercy from the mods
