Step 1: Understanding the Concept:
Gross Value Added (GVA) measures the contribution of economic sectors to the national economy.
Step 2: Detailed Explanation:
According to official estimates from the National Statistical Office (NSO) and the Economic Survey 2019-20, the agriculture and allied sector (crops, livestock, forestry, and fishing) contributed approximately $17.8\%$ of total national GVA at current prices.
This share falls within the $15\text{--}20\%$ bracket.
Step 3: Final Answer:
Therefore, the contribution of agriculture and allied sectors to India's GVA in 2019-20 was 15-20%.