Running several lower-voltage items from a higher-voltage supply
FYI Many proprietary LED lighting systems I've seen use 24v DC supplies to distribute power; low enough voltage to be safe, high enough to provide sufficiently efficient transmission without needing excessively thick cables. However, it's all relative: practically, it has an upper limit on what it can power before using mains voltage makes more sense.

As Jonk suggested, use buck converters, one for each set of LEDs. Ebay has many such modules for $1- $2 each that you could use. I just searched for "buck module adjustable" and searched by ascending price, and for $1 inc postage found one that accepts input of 4v-35v and output adjustable 1.25v to 30v. (Maximum input current 3A, I presume this should suffice), it is based on the LM2596 IC.

Using this approach has a major advantage: long wires are unlikely to be of concern: each buck module will happily take less than the 12v (reduced by cable losses) and maintain your preset output voltage). If not, simply use a higher supply voltage, say 24v, thicker wiring where necessary - but for safety reasons, consider heat produced by the wiring (and everything else). Installations may be legally required to be installed by an electrician; even low voltages, partly for this reason).

At the same time, PSUs (wall warts) are so cheap, I'd have recommended you just buy one for each LED unit assuming nearby sockets - except getting ones with 1.5v output is rare AFAIK and might incur a premium. But since you seem willing to consider various alternatives, and time less critical than other factors, I would suggest, as an alternative to my above suggested solution that you reconsider alternatives to the torches; they don't seem compellingly compatible with your overall requirements.