Fifteensquared

A puzzle where no clue poses any especial difficulty. I solved 21dn first even as my eye took it in.  I got 5, 6, 7, 8, 14, 17 and 24 in the Down set before moving on to the Across set where 4, 12, 13, 15 and 28 fell first. I completed the right half of the grid first. The very last clue was 18dn.

Many clues such as the following have familiar wordplay: Across: 10, 13, 20, 30 and Down: 5, 11, 14, 24

Across

1  WAY OUT - way-out (unconventional) sans the hyphen  
9 TARTAR - tar, tar -  I suspect that ‘Salt’ is a misprint for ‘Salts’ which will give salt (tar), salt (tar).
10 SUNDRIES - sun (’heat source’) dries - The repetition of the word ‘heat’  might have been avoided
13 ORDEAL- or (gold), deal
15 THIN - hidden in boTH INstances
16 SPLENDIDLY - (Len, did, l) in spy
19 GREENHOUSE - green, house - at the time of solving I took ‘family’ to be a nounal adj. qualifying ‘place’, only now do I see that the def. is ‘place to cultivate plants’ and that we have to get ‘house’ from ‘family’ (as in the ‘house of the Montagues’)
20 SCAR - s,car
23 ROCOCO - ro in C0 (company), CO (Commanding Officer)
25 ORIENTAL - or(i.e. nt)al - nt is got by deleting o from not - The clue as a whole has rather tricky wordplay 
27 ARCHIVES - arch(iv)es*
28 HAMLET - ham, let - good surface reading
29 ETERNITY - eternit*,y - y after anag. of (enter it)
30 STONED - two def.

Down

1 WITHOUT - wit (brains), h (hard), out 
2 YORKSHIRE - anag. of (His yorker)
3 USABLE - (-yo)u, sable
6 EL DORADO - el, do, rado* (anag. of road)
8 DISPLAY - dis (rev. of Sid), play
11 STEPSON - steps on (walks over)
14 LEISURE - lei, sure
18 INACTION - in, action (fighting) -
19 GARBAGE - b (born) in garage
21 RELATED - two def - As this is a linked clue, I believe, there must be three dots after the word ‘kin’ .
22 REPAST - re, past - Why four dots, I wonder. Three dots would suffice.
24 CACHE - hom. of cash
26 DEFT - d,e, FT (the paper)