15 gal. honey tangerine/other trees in 7-15gal

[StillHope]

1. I got 15 gal Honey tangerine at PlantitHawaii on Saturday.Unfortunately it was the only one and has a lot of mostly treated infestation. I had already arranged for a private delivery and was also told that the tree that big (over 5 feet tall) is hard to kill.At home I found a couple of other types of infestation.Scab on leave and couple of fruits .I probably made a big mistake (the tree is very expensive) but I need to know if it's not a big deal on this size of a tree.
What I could identify from this and other sources
(http://www.ctahr.hawaii.edu/nelsons/Misc/)-see "citrus" :

black flies (looks like treated successfully,but was a heavy infestation);
citrus scab (not sure if treated or treated enough)- not too much;
Elsinoe (fungal scab) - not too much;

greasy spot(http://edis.ifas.ufl.edu/hs141) -plenty but looks like treated.
White fly eggs?-wite spot at the back of the leaves with some cluster on it - could be treated also but not sure.
And quite a bit of distorted leaves - quite common problems from mites.

Saw also dead aphids but even alive it's not a big deal.

BUT - despite of all that the tree looks pretty good.
Has lots of fruit,the biggest are 1.5-2 inches.
I removed a lot of problem leaves and sprayed it with neem oil and put it by the canopy to move it out of the heavy rain if necessary.

So my question is - is it true that the tree that big would survive all of it?
Did anyone have to deal with 15 gal citrus with similar problems?

Should I keep it in pot for a while or plant as soon as possible?

2. I think most of people wouldn't buy the expensive tree with such problems.So not really expecting much help.
But would appreciate any advice on planting and growing a tree came in a big pot size (7 or 15 gal ).