15 ohms seems a little low but the clutch coil doesn't have a lot of resistance. I was thinking around twice that but I'm not sure of the spec at the moment and 15 ohms may be just fine. If you put power directly to the coil lead you should be able to hear an audible snap as it engages (engine off). If not you can safely assume the clutch coil is shot. Usually they fail in operation and not from sitting but in such a salty environment as the Keys I'd think it would become more likely. FYI, if the clutch coil is bad, you can do the job without opening the system. With the mounting bolts out the compressor will tilt down enough to get the clutch snap rings on and off. Make sure to not lose the shims that set the clutch air gap, they are small, thin, and easily misplaced. If yours is anything like the last one I did, you'll curse the cap screw phillips that hold the bracket to the top of the compressor. If you opt for a new clutch it will come with hex head phillips screws that should have been there in the first place.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff