That's not ori TRD rims btw.

Real TRD rims are made in Japan and lightweight forged rims. That one however is not made in Japan and normal casting rims. At size 15x6, the weight is still about 7kg. For comparison, my forged Japan rims also weigh 7kg but at much bigger size 17x8.5. If forged Japan rims for smaller sizes like that, the weight should only be around 4-5kg. You can also just check in TRD Japan website, they don't have that model listed there! Rather than buying that rims, better just buy Lenso or Advanti rims made in Taiwan which are still much lighter and have much better designs.

Well TRD can subcon their rims to any rim manufacturer, some fo their rims are also made by Rays. Just like NISMO whose rims are made also by Rays, and Prodrive rims (like mine) made by Bridgestone Japan. That Vios TRD rims are probably some low end rims which they stick a TRD sticker/cap on it. If made by Enkei then surely just one of their lowest product range, hence still heavy and not really listed in the TRD website.
Correct , Lenso is a Thailand brand but still decent quality with medium weight and many good designs. Advanti is from Taiwan but many of their rims are made by Enkei Taiwan and pretty light too, so good value for money.

Advantages:
- quicker acceleration
- better fuel economy
- better braking
- less tasking on suspension components due to less unsprung weight.

Disadvantages:
I believe none! Of course provided that the lighter rims do not compensate the strength which how a properly made lightweight rims should be anyway.