The minimum for considering a purchase is 400 nits and sRGB coverage. IPS is fine (preferably semi-matte), as OLED tends for have PWM and lower battery life due to lower nits per Watt efficiency (PHOLED is going to help here).
By targeting the budget category, the Gram Book 15 loses all the selling points that make the Gram series so special in the first place. The few redeeming qualities aren't enough to make the system an easy recommendation.