Reasonable.. calcidiol (25-hydroxyvitamin D3) has a half-life of about 15 days in the human body.
D3 is also stored in fat, and released as fat is metabolized.
doubtful, the body stores vitamin d in fat cells and individuals that have have sufficient levels will also have some stored up. Vitamin D levels in the blood don't work like an on/off switch depending on how long you were in the sunlight on a specific day or even week.