就是 (jiùshì) is one of the many "even ifs". Like 即使 , 就算 and 哪怕 it is used to introduce a hypothetical statement, which can then disregarded with 也.
Basic Structure
就是 + Hypothetical Statement + 也 + Action
Examples
Jiùshì zhè tái diànnǎo jiàɡé shànɡwàn, wǒ yě huì mǎi.
就是 这 台 电脑 价格 上万，我 也 会 买。Even if this computer's price is over 10,000 yuan, I'm still going to buy it.
Jiùshì jiànɡwēn le, wǒ yě yào chuān rèkù, shíshànɡ mɑ!
就是 降温 了，我 也 要 穿 热裤，时尚 嘛!Even if it's starting to get cooler, I'm still going to wear short shorts. It's the fad!
Jiùshì tā biànchénɡ yíɡè qiónɡɡuānɡdàn, wǒ yě yuànyì ɡēn tā zài yìqǐ.
就是 他 变成 一个 穷光蛋，我 也 愿意 跟 他 在 一起。Even if he were penniless, I would still be willing to be with him.
Note that the clause used after 就是 must be hypothetical, otherwise 虽然 should be used:
现在 虽然 是 高峰期，但 我 也 要 出去。
现在 就是 是 高峰期，我 也 要 出去。(wrong sentence)
In the sentence above, it being rush hour is not a hypothetical statement, so it is incorrect to use 就是.