To get max pressure into your RO
unit it should be plumbed into main water line into house (pressurised), if it's plumbed in after the storage tank (gravity feed), pressure will be considerably lower. They are slow and even slower when it's cold.
I would put new filters in (CCB and micron) so you know the age of them, they have a useful life of about 6 months (May vary by unit). If the RO
membrane needs replacing this can also seriously reduce flow. The membranes normally last around 4 years depending on care, flushing and use etc.
As posted above, quick depletion of DI
resin indicates RO
membrane has past useful life.