How often does your monstera produce a new leaf? Once/wk, every day, etc..?
Generally slow. Big leaves can take a long time to grow.
In the winter, indoors, mine hardly grows. Outside, in the growing season, it grows fairly fast!
That is true, outside in the warmer weather they will grow faster. They do enjoy heat and humidity. Indoors as a houseplant they'll grow slower all year. The amount and quality of nutrients you give them count for something too.
Can anyone quantify slow? That's pretty vague. What exactly is slow? How many inches of stem per week? Leaves? This is indoors of course; growing season and fall/winter. Mines slowwwwwwwwwww. I'm trying to figure out if a single leaf in 3 months is anywhere near the norm. If it is I'm out this is worse than bonsai from seed.
What are the conditions for the plant? Sun, temperatures, humidity, pot size, soil conditions, feeding practices, etc.? All these factors will affect growth--as will the time of year. As I said, I do see a big difference with this species depending on whether it is inside or out. Outside (in partial sun and higher temperatures), it can put out 2-3 new leaves per week and is an aggressive climber with freely forming aerial roots. Inside, under florescent in the basement maybe one leaf every two weeks. Leaves formed outside will also be much larger compared to those in the house. Post a pic so you can get feedback on pot size relative to the plant. If your plant is growing at a glacial rate throughout the year, it is lacking something.