Iso push or flat call with 77 in EP facing shorties shove?

[Hoop Addict]

$70 live tourney, 60 runners, down to about 27 or 28... table of 9.

Just after the 1st break, blinds at 200/400. I'm UTG+1 with 77. Lagish UTG shoves his shortstack for about 1500 total. I have ~9500 & would be a top 5 stack currently.

My table is generally passive, and I've only shown down strength, while UTG is fresh new to the table (I know he's laggy from previous & online experience with him). All other stacks at the table are between 3K and 6K with SB has 4600 and the BB (who is very tight) has about 4K.

Am I calling the 1500 or just iso-shoving? If I call 1500, would I be committed to calling, say a 5K stack if they push over me?