Is their actual agreement "15-17 HCP, any shape"?
The Blue Book says:
Quote
4 B 1 Passes and bids
Unless it is announceable (see 4D, 4E, 4F and 4G), a pass or bid must be alerted if it:
(a) is not natural; or
(b) is natural but has a potentially unexpected meaning.
So the question arises as to whether this is natural.
Quote
4 C 1
(b) A bid of no trumps which shows a preparedness to play in no trumps, and which conveys
no unusual information about suit holdings; it must not be forcing unless a forcing
auction has already been created. Note that certain ostensibly natural no trump bids are
permitted to allow a shortage by agreement
Do we expect that someone with a 6-2-5-0 hand is really prepared to play in no trumps? If not, it's alertable.
Did 2
♣ establish a forcing auction? If not, and 2NT is forcing, then it's alertable.
BTW, even though the void in partner's suit is a misfeature, that hand still looks like much more than 17 HCP, IMHO.