A watering schedule (how often to water) depends on the type of potting medium in use and how quickly it dries out. The soil should be thoroughly saturated until water is freely exiting the drainage holes and the pot should be allowed to drain before placing it back on it's saucer. The soil moisture can be checked again in five to seven days by sticking a finger down a few inches into the soil. If it's still moist/damp, hold off on adding additional water and check again in another couple of days. The plant roots should be kept barely moist, not sopping wet to the point where they rot but not so dry that the roots wither and die. It's all a learning experience with getting to know the type of plant, it's growing requirements for light, temperature and moisture, etc. and paying attention to the soil and how quickly it dries.
To my eyes, the soil in your photos appears to be quite dense and water retentive, which would allow the plants to go longer periods between watering but you say you water every 1.5 to 2 weeks which makes me think you are not watering thoroughly enough to saturate the soil and roots.
