For 15mm keep an eye on Khurasan especially over the coming months, all the above ranges are indeed very good (QRF does have a lot to choose from) but often a lot of the Ultra modern kit is missing, most stuff being veered towards cold war/1990s. Khurasan seemingly will be making more of the up to date kit, with his historical lines like Yom-Kippur being excellent stand ins for 3rd world states.
For fairly cheap 1/100 vehicles, if you come across Zvezdas 'Hot War' kit, they may be worth an investment, T-72s with added armour and BTRs, as well as Abrams and Bradleys.