[Mila]

You could buy 28 oz bottle - more than you need, but not too much as in several lbs
Check for smaller size of r-32 to get your extension piping - maybe you could use more than 15 feet of pipe- if there could be some advantage?

 

[Mila]

28oz bottle R-32?

Yes, they sell it -28.3 oz to be precise; not sure if I am allowed to post links.
Think it is not a good idea as some DIY may get in trouble.

Thought the guy is a small business owner. In some locations R-32 equipment is scarce
Small amounts could be handy sometimes - easier to charge homeowners (pun intended)