A washer usually fills slowly because something is blocking the water on its way in. The most common cause is a clogged screen where the hoses connect to the back of the washer. Hard water and sediment build up there over time.
First, make sure both water valves behind the washer are fully open. Also check the fill hoses for kinks. If every faucet in your home is slow, the problem is your water pressure, not the washer.
To check the screens, turn off the water and unscrew the hoses. If they look clogged, the inlet valve usually needs replacing, since cleaning can push debris into the valve and cause leaks.